The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Nuclear reactors, such as boiling water reactors, generally include a reactor core comprised of many fuel bundles through which, and around which, a liquid moderator or coolant, e.g., liquid water, flows. Nuclear reactions within the fuel bundles generate heat used to convert the coolant to steam as the coolant passes through the core. The steam is then used to generate electrical power. Each of the fuel bundles typically includes a plurality of sealed and vertically upstanding fuel rods housed within an elongate tubular channel. Within the channel, the fuel rods of each fuel bundle are held in a spaced apart configuration by two or more spacer grids comprised of a plurality of interconnected spacers that form a plurality of rows and columns of open cells. Each cell has a respective one of the otherwise long and flexible fuel rods extending therethrough and serves to prevent the fuel rods from coming into abrading contact one with another under the dynamics of coolant flow within the reactor. The spacers additionally maintain the designed fuel-rod-to-fuel-rod spacing for optimum nuclear performance and promote mixing of the moderator.
The fuel rods are generally a monolithic structure having a length substantially equal to the overall length of the respective bundle. Additionally, each of the fuel rods typically includes an inner axial bore extending approximately the entire length of the respective rods. Nuclear fuel, e.g., uranium 235, is deposited within the inner bore to generate the nuclear reaction. Accordingly, the enrichment level of the fuel within each such fuel rod is generally consistent along the length of the rods.
Additionally, most known spacers have very complex designs that can impede the flow of coolant through the respective bundle and often entrap debris flowing though the bundle. Such entrapped debris can vibrate, flap or rattle against the fuel rods due to the coolant flow and damage fuel rods, causing potential exposure of the fuel to the water in the reactor.